<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport"
        content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .box {
            margin: 0;
            padding: 0;
            -webkit-box-sizing: border-box;
            box-sizing: border-box;
            width: 100%;
            margin: 0 auto;
            max-width: 980px;
            min-width: 320px;
        }

        .box div:nth-child(1) {
            float: left;
            width: 50%;
            height: 300px;
            background-color: yellow;
        }

        .box div:nth-child(n+2) {
            float: left;
            width: 25%;
            height: 300px;
            background-color: violet;
        }

        .box div:nth-child(3) {
            background-color: turquoise;
        }
    </style>
</head>

<body>
    <div class="box">
        <div></div>
        <div></div>
        <div></div>
    </div>
</body>

</html>